INTERNATIONAL STANDARD

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1 INTERNATIONAL STANDARD IEC First edition Power transformers Part 10: Determination of sound levels Transformateurs de puissance Partie 10: Détermination des niveaux de bruit IEC 2001 Copyright - all rights reserved No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. International Electrotechnical Commission 3, rue de Varembé Geneva, Switzerland Telefax: inmail@iec.ch IEC web site Commission Electrotechnique Internationale International Electrotechnical Commission PRICE CODE V For price, see current catalogue

2 IEC:2001(E) CONTENTS FOREWORD...3 INTRODUCTION Scope Normative references Definitions Instrumentation and calibration Choice of test method Load conditions General No-load current and rated voltage Rated current and short-circuit voltage Reduced-load current Principal radiating surface General Transformers with or without cooling auxiliaries, dry-type transformers in enclosures and dry-type transformers with cooling auxiliaries inside the enclosure Cooling auxiliaries mounted on a separate structure spaced 3 m away from the principal radiating surface of the transformer Dry-type transformers without enclosures Prescribed contour Microphone positions Calculation of the area of the measurement surface Measurements made at 0,3 m from the principal radiating surface Measurements made at 2 m from the principal radiating surface Measurements made at 1 m from the principal radiating surface Measurements on test objects where safety clearance considerations require a measurement distance which for all or part of the prescribed contour(s) exceeds the provisions of 10.1 to Sound pressure method Test environment Sound pressure level measurements Calculation of average sound pressure level Sound intensity method Test environment Sound intensity level measurements Calculation of average sound intensity level Calculation of sound power level Addition of no-load and load current sound power levels Far-field calculations Presentation of results...20 Annex A (informative) Narrow-band and time-synchronous measurements...29 Annex B (informative) Typical report of sound level determination...31

3 IEC:2001(E) 3 INTERNATIONAL ELECTROTECHNICAL COMMISSION POWER TRANSFORMERS Part 10: Determination of sound levels FOREWORD 1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising all national electrotechnical committees (IEC National Committees). The object of the IEC is to promote international co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and in addition to other activities, the IEC publishes International Standards. Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work. International, governmental and non-governmental organizations liaising with the IEC also participate in this preparation. The IEC collaborates closely with the International Organization for Standardization (ISO) in accordance with conditions determined by agreement between the two organizations. 2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an international consensus of opinion on the relevant subjects since each technical committee has representation from all interested National Committees. 3) The documents produced have the form of recommendations for international use and are published in the form of standards, technical specifications, technical reports or guides and they are accepted by the National Committees in that sense. 4) In order to promote international unification, IEC National Committees undertake to apply IEC International Standards transparently to the maximum extent possible in their national and regional standards. Any divergence between the IEC Standard and the corresponding national or regional standard shall be clearly indicated in the latter. 5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any equipment declared to be in conformity with one of its standards. 6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights. International Standard IEC has been prepared by IEC technical committee 14: Power transformers. This first edition of IEC cancels and replaces IEC 60551, published in 1987 and its amendment 1 (1995), and constitutes a technical revision. The text of this standard is based on the following documents: FDIS 14/390/FDIS Report on voting 14/394/RVD Full information on the voting for the approval of this standard can be found in the report on voting indicated in the above table. This publication has been drafted in accordance with the ISO/IEC Directives, Part 3. Annexes A and B are for information only. IEC consists of the following parts, under the general title: Power transformers. Part 1: General Part 2: Temperature rise Part 3: Insulation levels, dielectric tests and external clearances in air

4 IEC:2001(E) Part 5: Ability to withstand short-circuit Part 8: Application guide Part 10: Determination of sound levels The committee has decided that the contents of this publication will remain unchanged until At this date, the publication will be reconfirmed; withdrawn; replaced by a revised edition, or amended. A bilingual version of this publication may be issued at a later date.

5 IEC:2001(E) 5 INTRODUCTION One of the many parameters to be considered when designing and siting transformers, reactors and their associated cooling equipment is the amount of sound that the equipment is likely to emit under normal operating conditions on site. Sources of sound The audible sound radiated by transformers is generated by a combination of magnetostrictive deformation of the core and electromagnetic forces in the windings, tank walls and magnetic shields. Historically, the sound generated by the magnetic field inducing longitudinal vibrations in the core laminations has been dominant. The amplitude of these vibrations depends on the flux density in the laminations and the magnetic properties of the core steel, and is therefore independent of the load current. Recent advances in core design, combined with the use of low induction levels, have reduced the amount of sound generated in the core such that the sound caused by the electromagnetic forces may become significant. Current flowing in the winding conductors produces electromagnetic forces in the windings. In addition, stray magnetic fields may induce vibrations in structural components. The force (and therefore the amplitude of the vibrations) is proportional to the square of the current, and the radiated sound power is proportional to the square of the vibrational amplitude. Consequently, the radiated sound power is strongly dependent on the load current. Vibrations in core and winding assemblies can then induce sympathetic vibrations in tank walls, magnetic shields and air ducts (if present). In the case of dry-type, air-cored shunt or series reactors, sound is generated by electromagnetic forces acting on the windings in a similar manner to that described above. These oscillatory forces cause the reactor to vibrate both axially and radially, and the axial and radial supports and manufacturing tolerances may result in the excitation of modes in addition to those of rotational symmetry. In the case of iron-cored reactors, further vibrations are induced by forces acting in the magnetic circuit. For all electrical plants, the consequence of the presence of higher harmonics on the power supply should be understood. Normally, vibrations occur at even harmonics of the power frequency, with the first harmonic being dominant. If other frequencies are present in the power supply, other forces may be induced. For certain applications, this may be significant, particularly because the human ear is more sensitive to these higher frequencies. Any associated cooling equipment will also generate noise when operating. Fans and pumps both tend to generate broad-band noise due to the forced flow of air or oil. Measurement of sound This is a preview - click here to buy the full publication Sound level measurements have been developed to quantify pressure variations in air that a human ear can detect. The smallest pressure variation that a healthy human ear can detect is 20 µpa. This is the reference level (0 db) to which all the other levels are compared. The perceived loudness of a signal is dependent upon the sensitivity of the human ear to its frequency spectrum. Modern measuring instruments process sound signals through electronic networks, the sensitivity of which varies with frequency in a manner similar to the human ear. This has resulted in a number of internationally standardized weightings of which the A- weighting network is the most common. Sound intensity is defined as the rate of energy flow per unit area and is measured in watts per square metre. It is a vector quantity whereas, sound pressure is a scalar quantity and is defined only by its magnitude.

6 IEC:2001(E) Sound power is the parameter which is used for rating and comparing sound sources. It is a basic descriptor of a source s acoustic output, and therefore an absolute physical property of the source alone which is independent of any external factors such as environment and distance to the receiver. Sound power can be calculated from sound pressure or sound intensity determinations. Sound intensity measurements have the following advantages over sound pressure measurements: an intensity meter responds only to the propagating part of a sound field and ignores any non-propagating part, for example, standing waves and reflections; the intensity method reduces the influence of external sound sources, as long as their sound level is approximately constant. The sound pressure method takes the above factors into account by correcting for background noise and reflections. For a detailed discussion of these measuring techniques, see IEC , Part 10-1: Determination of transformer and reactor sound levels User guide (under consideration)

7 IEC:2001(E) 7 POWER TRANSFORMERS Part 10: Determination of sound levels 1 Scope This part of IEC defines sound pressure and sound intensity measurement methods by which sound power levels of transformers, reactors and their associated cooling auxiliaries may be determined. NOTE For the purpose of this standard, the term "transformer" means "transformer or reactor". The methods are applicable to transformers and reactors covered by the IEC series, IEC 60289, IEC and the IEC series, without limitation as regards size or voltage and when fitted with their normal cooling auxiliaries. This standard is primarily intended to apply to measurements made at the factory. Conditions on-site may be very different because of the proximity of objects, including other transformers. Nevertheless, the same general rules as are given in this standard may be followed when on-site measurements are made. 2 Normative references The following normative documents contain provisions which, through reference in this text, constitute provisions of this part of IEC For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this part of IEC are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of IEC and ISO maintain registers of currently valid International standards. IEC (all parts), Power transformers IEC 60289:1988, Reactors IEC 60651:1979, Sound level meters IEC 60726:1982, Dry-type power transformers IEC 61043:1993, Electroacoustics Instruments for the measurement of sound intensity Measurement with pairs of pressure sensing microphones IEC (all parts), Convertor transformers ISO 3746:1995, Acoustics Determination of sound power levels of noise sources using sound pressure Survey method using an enveloping measurement surface over a reflecting plane ISO :1993, Acoustics Determination of sound power levels of noise sources using sound intensity Part 1: Measurement at discrete points